Hybrid and electric vehicles commonly demand significant amounts of energy from a high voltage traction battery. The energy may be used to drive motors and electrical accessories. The traction batteries can include a large number of interconnected battery cells. Maintaining battery temperature within a desired operating range may promote proper battery function and enhance battery longevity. Also, it may be beneficial to limit the differential in temperature across individual cells. Thermal management devices may be used to regulate battery temperature. For example, directing passenger cabin air or external air across a battery may help regulate temperature. Additionally, electric heating systems may be used to warm a battery during low temperature conditions.